The present invention relates in general to manufacturing lines for manufacturing heat exchangers used in automotive air conditioners, each heat exchanger comprising a plurality of parallel flat heat extending tubes arranged to constitute a rectangular mass, a plurality of outer fins alternatively arranged in the mass of the flat heat extending tubes and two header pipes connected to opposed sides of the mass. More particularly, the present invention relates to the heat exchanger manufacturing lines of a type which comprises a header pipe producing device which produces the header pipes by pressing or curling flat metal plates, a flat tube producing device which produces the flat heat exchanging tubes each including an elongate flat metal tube and an elongate inner metal fin installed in the flat tube, an outer fin producing device which produces the outer fins by corrugating an elongate metal plate, and assembling devices which produce the heat exchangers one after another by assembling the header pipes, the elongate flat tubes and the outer fins. More specifically, the present invention is concerned with workpiece handling devices arranged in the heat exchanger manufacturing line, which handle the workpieces or flat heat exchanging tubes for assisting the operation of the above-mentioned producing and assembling devices.